On 2023-12-01 21:52, Bruno Haible wrote:
There is nothing wrong with this code (m4/frexp.m4:159, m4/frexpf.m4:83).
Isn't there? I thought that the C standard doesn't let you access a
'double volatile' object via a 'void *' or 'void const *' pointer. It'd
need to be 'void volatile *' or 'void const volatile *'.
We don't want to add a cast here, because — as Paul argues — casts can make
code more difficult to maintain in the long run.
We can conform to standard C without a cast with something like the
attached (which I haven't installed).
(I assume the 'volatile' is there because of the funky things compilers
do with x86 double....)From 006cf2337a8ca2e3a0b41c488fbe3d95eda201f3 Mon Sep 17 00:00:00 2001
From: Paul Eggert <egg...@cs.ucla.edu>
Date: Fri, 1 Dec 2023 22:19:22 -0800
Subject: [PATCH] frexp: pacify clang re address-of-volatile
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Problem reported by Sam James in:
https://lists.gnu.org/r/bug-gnulib/2023-12/msg00013.html
* m4/frexp.m4 (gl_FUNC_FREXP_WORKS): Don’t try to convert
‘double volatile *’ to ‘void const *’ as the C standard
doesn’t allow accessing volatile variables through
pointer-to-nonvolatile.
---
ChangeLog | 8 ++++++++
m4/frexp.m4 | 5 +++--
2 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index c713de7b42..f30430d3de 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,13 @@
2023-12-01 Paul Eggert <egg...@cs.ucla.edu>
+ frexp: pacify clang re address-of-volatile
+ Problem reported by Sam James in:
+ https://lists.gnu.org/r/bug-gnulib/2023-12/msg00013.html
+ * m4/frexp.m4 (gl_FUNC_FREXP_WORKS): Don’t try to convert
+ ‘double volatile *’ to ‘void const *’ as the C standard
+ doesn’t allow accessing volatile variables through
+ pointer-to-nonvolatile.
+
Update portability doc for CHERI, C23
* doc/gnulib-readme.texi:
Prefer “null pointer” to “@code{NULL}” since C23 has nullptr.
diff --git a/m4/frexp.m4 b/m4/frexp.m4
index 0293765c59..b23aa470c3 100644
--- a/m4/frexp.m4
+++ b/m4/frexp.m4
@@ -1,4 +1,4 @@
-# frexp.m4 serial 18
+# frexp.m4 serial 19
dnl Copyright (C) 2007-2023 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
@@ -156,7 +156,8 @@ int main()
{
int exp;
double y = frexp (x, &exp);
- if (memcmp (&y, &x, sizeof x))
+ double x1 = x;
+ if (memcmp (&y, &x1, sizeof x1))
result |= 4;
}
return result;
--
2.40.1
